What if Balthazar Charles of Spain Hadn't Died?

In 1646, Balthazar Charles, Prince of Asturias and heir to the Spanish throne died at the age of 16 of smallpox. As he had no surviving siblings and his mother had died his father Phillip IV remarried and had children with his niece Maria Anna, with the only child to outlive their father being the horrifically inbred Charles II. His death without issue while leaving the throne to the House of Bourbon would set off the War of the Spanish Succession, leading to the loss of most of the Habsburg family's western European holdings.

So what I'm wondering is if the heir hadn't died, what might have been the fate of the Spanish Habsburgs? How long may they have held the throne, and how might this prolonged Habsburg power have changed Europe?
I think there's just as much a chance of Balthazar Charles and Maria Anna's children, or their children's children (if any survive), of being just as inbred as OTL Charles II. In other words, the outlook still doesn't look too good for the Spanish Hapsburgs.